Suppose and is negative. Here are some small variations on the previous problems:
Can someone please point me in a direction towards solving this problem, I am not sure what they are asking?
You can also note that a right triangle with hypotenuse of length 13 and one leg of length 5 has cosine of the angle between those two side 5/13. What is the length of the other leg? And from that, what is the sine of the angle? This is treating the angle as between 0 and . Use the quadrant information to find the sign.